There are a variety of applications in which it is important for a user to be able to determine readily the amount of a product which remains in a dispensing container. As an example, with respect to which the invention will be specifically described hereinafter, it is known to package nitroglycerin in a metering aerosol-type dispenser so that when a dose is to be administered it can be sprayed directly into the mouth of the user. Typically the spray device is arranged so that a full single dose is administered by one depression of an axially reciprocable button at the top of the container. Such pharmaceutical material is indicated for use in many cases of angina.
Since the container of the nitroglycerin is generally of high opacity, either due to the optical nature of its walls or to the application of opaque labels to the walls, the user cannot at all times see how much of the nitroglycerin remains in the container. This can be highly disadvantageous, particularly if the user is planning to be away from other sources of supply of nitroglycerin for a substantial period of time, and cannot tell how much of the nitroglycerin remains in his dispenser. In such event it is possible that he will run out of nitroglycerin when he needs it badly, and when an alternate source is not readily available to him.
One method by which an approximation of the amount of flowable material remaining in the dispenser can be obtained is to place the container in water, for example in a bowl or sink of water. In one example of such use, a full canister containing approximately 200 doses will sink in the water; if the canister is 3/4 full, it will float with approximately a 1/4 of its volume protruding above the top of the water, and if about half full it will float with more of its volume above the water surface. When it becomes depleted to the extent that it is only about 1/4 full, or when it is empty, it tends to float at a variably oblique angle about half out of the water.
Such a method of indication of the quantity of product remaining in the container is obviously quite inaccurate. For example, typically it may be difficult to tell whether the canister is empty or has up to as much as 50 doses in it.
Knowledge of the quantity of product remaining in an aerosol dispenser, or in other types of dispensers, is obviously desirable in many other applications, whether in connection with pharmaceuticals or entirely different types of products.
Accordingly, it is an object of the invention to provide a new and useful method and apparatus for storing and dispensing flowable product from a container, and for indicating the quantity of such product which remains in the container at any given time.
Another object is to provide such method and apparatus in which the indications of remaining product quantity are sufficiently accurate for practical purposes.
A further object is to provide such method and apparatus which are very easy to use, and inexpensive to provide.